Hello,
And thank you for your replies Li_Ann and Firocks

.
I have been away due to 2 simple reasons:
The 1st is the best one which is that I`m still in vacations

The 2nd one, and the most serious one, is that I am going totally crazy and getting really really nervous as in 12 days I`ll know if I am going to college to the course I chose or not.. lots of waiting (yeah, being a student involves a lot of waiting around..

).
Now, regarding the gadgets, I have to say that I am really interested in some of them; almost all of them have some electronics or physics principle behind the way they work and I am really keen on trying to do the listening device gadget as it as an easy and useful physics/electronics principle behind it ( just like a microphone converts the difference of pressure in the air due to our voice into an electric signal that can be amplified, the gadget in question, converts the difference of trajectory of the laser beam due to the soundwaves..) but, it seems totally functional to me.
The main problem would be to solder the photo cell to the headphone pair, but I really want to try it